1. Field of the Invention
This invention relates to a method for relieving residual stress in an object, more particularly to a method using a vibration energy for relieving residual stress in an object.
2. Description of the Related Art
It is known in the art that the internal residual stress of an object can be relieved by applying a vibration energy thereto using a vibrator and that the internal residual stress is not directly relieved by the operating frequencies of the vibrator, but by excited harmonic vibrations of the metal object.
U.S. Pat. No. 4,823,599 discloses a method of operating a vibrator for the stress relief of a workpiece. The method includes the steps of determining, within a defined harmonics region, harmonics corresponding to those vibrations in an operating range in which resonances or similar stable states of vibration occur, and selecting a vibration speed, that causes the higher numbers of harmonics in the defined harmonics region, as the operating speed for the vibrator.
U.S. Pat. No. 4,968,359 discloses a method of stress reliving in metal objects. The method includes the steps of: applying a mechanical cyclic vibration energy to the metal object; identifying a plurality of orders of harmonic vibration absorption peaks, each consisting of a plurality of vibration absorption resonant peaks; and applying the mechanical cyclic vibration energy to the metal object for an extended period of time at a fixed frequency corresponding to a sub-harmonic frequency of one of the harmonic peaks. The sub-harmonic frequency associated with a particular order of the harmonics corresponds to a vibration amplitude equal to approximately one third of maximum vibration amplitude of the particular order.